Alloys in the form of metallurgical two-component or multi-component systems with a miscibility gap (monotectic), also called dispersion alloys, generally consist of metallic components of very different specific weight. The heavy components, such as Pb in AlPb dispersion alloys have a strong tendency to segregate, for instance during the solidification of the alloy. Initially more mixed crystals of a different concentration are separated than during the later stage of cooling, so that the mixed crystals from the melt are not homogeneous. The manufacture of AlPb materials for use in slide bearings under terrestrial conditions using casting techniques is therefore made impossible for instance by the miscibility gap existing in the AlPb system. The fine distribution of lead in an Al-matrix required for use in a slide bearing material is not reached.
In connection with the production of functional layers of such dispersion alloys, DE-OS 31 37 745 for instance discloses the manufacture of metal powders by atomization of a melt and its sintering onto a substrate. However, this method provides a very nonhomogeneous structure, so that the results fluctuate considerably when tested in a machine for slide-bearing testing. In addition, it had been found that as a result of the inner notch effect, the pores which are still present in the sintered layer cause cracking when the slide element is subjected to alternating loads
From DE-AS 15 08 856 a method is already known which requires the use of continuous casting for aluminum alloys with a high content of lead. Thereby, a homogeneous one-phase melt of an aluminum-lead alloy containing 20 to 50% lead is cast onto a metallic substrate to directly produce a composite bearing material. However, this method leads to a defective bond of the AlPb sliding layer (functional layer) with the steel. Moreover, in spite of cooling with water, separation takes place even in the mold, which means that the temperature gradient between the temperature of the homogeneous melt and the mold temperature is too small, so that the onset of the thermodynamic equilibrium can not prevented. The result is a sliding layer with a homogeneous, segregated structure; a two-layered tribologically non-usable sandwich results, which in addition has the disadvantage of poor bonding with the substrate.
Also, from DE-PS 21 30 421 and DE-OS 22 41 628 methods for the production of composite metal strips are known, wherein molten aluminum exits through an opening in the bottom of a melting crucible and molten lead is guided in a thin, thread-like stream through the molten aluminum also in the opening in the bottom of the melting crucible. The melt mixture of for instance aluminum and lead formed in the bottom opening of the melting crucible is then vibrated and mixed by ga jets and blown onto the upper surface of a substrate travelling alongside. A functional layer produced this way is still nonhomogeneous to a large extent, whereby due to their much greater density the lead particles have a strong tendency to segregate and coagulate as the agitated stream of melt mixture is applied onto the surface of the substrate.
A method is known from DE-AS 22 63 268 wherein a melt mixture of lead and aluminum is laterally centrifuged in the form of fine particles by a rotor designed as a siphon and segregated on an impact wall where the material solidifies in the form of flakes (splatter cooling). However, due to its flake-shaped (leaf-shaped) structure, this material cannot be processed to a plating material, by extrusion or by powder rolling. During the production of molded parts using pressure and temperature (by means of isostatic presses), segregation occurs again, resulting in extensive nonhomogenity and consequently in unusability of AlPb solid bearings manufactured by this method.
In DE-OS 17 75 322 a slide bearing or a material for its manufacture is described, which consists of Al-alloys (e.g. dispersion alloys based on AlPb or AlSn), wherein the Al material which is later plated on steel serving as a substrate is manufactured by powder rolling. As a result of the compaction by powder rolling and of the subsequent rolling and plating operation, the Al bearing material made this way has a banded arrangement of the soft minority phase (e.g. Pb). Such a banded structure is a considerable disadvantage for slide bearings subjected to alternating loads, since permanent cracks are formed in the bands as a result of the inner notch effect.
PCT WO 87/04377 describes a process by means of which an AlPb strip with a thickness of 1 to 5 mm is produced and then plated onto steel serving as a substrate material. However, the fine lead distribution described therein is not achieved in practice, because due to the rolling-plating operation, the lead is distributed in bands and does not resume the globular form even during the subsequent heat treatment Besides, it has been found that segregation takes place already in strips which are thicker than 0.5 mm.
This drawback is avoided by DE-PS 37 30 862.9-16 which, while using a melt-spin process similar to the one described in WO 87/04377, has an AlPb foil having a maximum thickness of 0.5 mm and a very fine globular distribution of lead which is applied on a substrate by ultrasonic welding, by soldering or gluing thereby avoiding rolling operations.
However, it has been proven that the ultrasonic welding is an expensive and not particularly reliable procedure, while soldering and gluing are not suitable for the production by the strip method of semifinished materials to be used in slide bearings.